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First Result of Urumqi 6cm Polarization Observations:

Exploring Cygnus Loop through 6cm observations with detailed spectral index, rotation measures, and depolarization analysis. Results exhibit intricate spatial and spectral variations. A comprehensive study providing insights into this astronomical phenomenon through new maps and parameters analysis.

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First Result of Urumqi 6cm Polarization Observations:

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  1. First Result of Urumqi 6cm Polarization Observations: New 6cm Maps of Cygnus Loop Xiaohui Sun, Wolfgang Reich JinLin Han, Patricia Reich, Richard Wielebinski Partner Group of MPIfR at NAOC

  2. Outline • Introduction to the Cygnus Loop • Previous results at radio band • New 6cm observations and results • System and observational parameters • New 6cm map of the Cygnus Loop • Spectral index map • Rotation Measure results • Depolarization analysis • Conclusions

  3. Introduction to the Cygnus Loop • Location: • little obscuration from the Galactic plane • Size: ~ • ideal for Urumqi 25m dish at 6cm • Distance: 540 pc (HST observation) • Very precise • nearby and hence little confusion by local medium • Age:~14,000 yr • just transition from adiabatic to radiative phase • Appearance: (Cavity explosion, interaction with cloud?) • bright NE and WEST shells at radio, optical and X-ray • bright south shell at radio

  4. Previous Results at Radio Band • Spectral index – need high frequency total intensity data • integrated flux density • 11cm, 20cm and 35cm data =-0.420.06 (Uyaniker et al. 2004) • 6cm flux density: 73Jy spectral steepening(Kundu & Becker 1972) • spatial variation over the SNR and spectral curvature • 408MHz, 1420MHz and 2695MHzdatalarge spectral variation (Green 1990; Leahy & Roger 1998) • NOT supported by high quality data(Uyaniker et al. 2004) • Polarization – need high frequency polarization data • rotation measure • south part: -20 rad/m2 (Uyaniker et al. 2002; Kundu & Becker 1972) • depolarization at the northern part • NE region, internal depolarization (Leahy et al. 1997) • Appearance • substantial difference between the south and the north part two-SNR scenario (Uyaniker et al. 2002)

  5. Spectral index of flux density: -flux density -frequency • Spectral index of brightness temperature:

  6. Previous Results at Radio Band • Spectral index – need high frequency total intensity data • integrated flux density • 11cm, 20cm and 35cm data =-0.420.06 (Uyaniker et al. 2004) • 6cm flux density: 73Jy spectral steepening(Kundu & Becker 1972) • spatial variation over the SNR and spectral curvature • 408MHz, 1420MHz and 2695MHzdatalarge spectral variation (Green 1990; Leahy & Roger 1998) • NOT supported by high quality data(Uyaniker et al. 2004) • Polarization – need high frequency polarization data • rotation measure • south part: -20 rad/m2 (Uyaniker et al. 2002; Kundu & Becker 1972) • depolarization at the northern part • NE region, internal depolarization (Leahy et al. 1997) • Appearance • substantial difference between the south and the north part two-SNR scenario (Uyaniker et al. 2002)

  7. System and Observational parameters Frequency: 4.8 GHz Bandwidth: 600 MHz Tsys: 22 K-25 K HPBW: 9.5 arcmin First Sidelobe: 2% Instrumental polarization: peak 0.5% ring: 2% Tracking error: <1 Map Center: (20h52m, 3030) Map Size: 4.2 4.8 Scan velcity: 2/min Scan separation: 4 Integration time: 2 min/pixel Scan direction: RA and DEC Observation Date: 8/2004-12/2004 Coverages I (PI): 5 (6)

  8. New 6cm Map Reduction spike and interference scanning effects calibration combine data HPBW (CL2): 9.7 arcmin r.m.s-I: 1 mK TB (0.6) r.m.s-PI: 0.4 mK TB (0.35) CL2 CL4

  9. CL4 (2048+312): Variable extragalactic origin, z=3.18 angular broadening time scale: 48 days variation: 30%

  10. C 25% NE2 20% W 20% NE1 15% S1 20% S2 25% S3 20% New 6cm Map

  11. Effelsberg 11cm and 21cm Map

  12. Effelsberg 11cm and 21cm Map

  13. Spectral index: integrated flux density New measurement Integrated flux density: 90 9 Jy 20% larger than previous value (miss diffuse component) Consistent with Uyaniker et al (2004) No spectral steepening or flattening until 5 GHz

  14. Spectral index Map: 6cm/11cm/21cm • zerolevel (TT-plot) • 6cm +2 mK • 11cm +8 mK • 21cm +23 mK • limit: ~20 r.m.s • high signal-to-noise ratio • influence of background • spectral index variation • NE, SW, NW, CL4: -0.4 • Increase towards diffuse region, maximal difference ~0.3, support Uyaniker et al. (2004) • Qualitatively explanation In diffuse region: magnetic field less compressed, high energy electrons contribute

  15. 6cm/11cm- 6cm/21cm • spectral curvature • >0: flattening • <0: steepening • Difference map: | |<0.15 • south, NW, NE: >0 • Middle: <0 • NO spectrum curvature support Uyaniker et al. (2004)

  16. Rotation Measure results: South • Calculation: linear fitting the PAs at 6cm, 11cm and 21cm (PI > 5r.m.s) • Results: South part • -21 rad/m2 • Rotation of PA ~4 • intrinsic magnetic direction • magnetic field along the shell • Consistent with previous results • Foreground contribution ne=0.02 cm-3, B||=-3G, D=540 pcRM=-26 rad/m2

  17. Rotation Measure results: South • Calculation: linear fitting the PAs at 6cm, 11cm and 21cm (PI > 5r.m.s) • Results: Southern part • -21 rad/m2 • Rotation of PA ~4 • intrinsic magnetic direction • magnetic field along the shell • Consistent with previous results • Foreground contribution ne=0.02 cm-3, B||=-3G, D=540 pcRM=-26 rad/m2

  18. Rotation Measure results: North • Region C: • RM=-28 rad/m2 • Projection? • Region NE1, NE2 and W: • 21cm totally depolarized • Ambiguity n 362 rad/m2 • Average RM for three possibilities: • N=0: RM=-73 rad/m2 • N=-1: RM= 290 rad/m2 • N=1: RM= -430 rad/m2

  19. Rotation Measure results: North • Region C: • RM=-28 rad/m2 • Projection? • Region NE1, NE2 and W: • 21cm totally depolarized • Ambiguity n 362 rad/m2 • Average RM for three possibilities: • N=0: RM=-73 rad/m2 • N=-1: RM= 290 rad/m2 • N=1: RM= -430 rad/m2

  20. Rotation Measure results: North • Region C: • RM=-28 rad/m2 • Projection? • Region NE1, NE2 and W: • 21cm totally depolarized • Ambiguity n 362 rad/m2 • Average RM for three possibilities: • N=0: RM=-73 rad/m2 • N=-1: RM= 290 rad/m2 • N=1: RM= -430 rad/m2

  21. Minimum Rotation Measure Case (n=0)

  22. Large Rotation Measure Case (n=1):NE1+NE2 • Magnetic field: energy equipartition 47 G • Flux density: 11 Jy • Spectral index: -0.4 • Emission volume: 400 pc3 • Electron density: 1 cm-3pressure balance • 10-100 cm-3Optical filament observation • OVI (Long et al. 1992) • SII (Patnaude et al. 2002) • Several cm-3X-ray observation • ASCA (Miyata et al. 1994) • ROSAT (Lu & Aschenbach 2005) • Depth of the filament: 4.8 pc  RM=-128 rad/m2 strict lower limit by a factor of a few

  23. Large Rotation Measure Case (n=1)

  24. Depolarization Analysis • Description of depolarization: • Depolarization mechanism: • Bandwidth depolarization: • Internal depolarization: • External depolarization: • Beam depolarization • Similar to external depolarization • Depends on the resolution • Polarization angle changes in the scale of beam size

  25. Depolarization Analysis • Bandwidth depolarization NOT important • =600 MHz @ 6cm • =40 MHz @ 11cm • =20 MHz @ 21cm • Beam depolarization is NOT important • No distortions in polarization angle maps • Depolarization does not depend on the resolution (both at 10 arcmin and 1 arcmin)

  26. Depolarization Analysis • Southern part and C filament • Observation: PC6cm~PC11cm~PC21cm • Explanation: no depolarization • Northern part • Observation: • DP21cm~0 • NE1: PC6cm~27% PC11cm~23% • NE2: PC6cm~28% PC11cm~23% • W: PC6cm~20% PC11cm~15% • Minimal RM case (-73 rad/m2): DP6cm=94% DP11cm=50% • Large RM case (-430 rad/m2): DP6cm~0 • Large RM case (290 rad/m2): DP6cm=33% DP11cm=12%

  27. Remarks on Two-SNR picture Different properties between the northern part and the southern part at: radio (new observations) other bands (X-ray, optical, …) Interaction of the two SNR: Similar distance no enhancement in the overlap (SNRs DEM L316 in LMC Williams et al. 1997)

  28. Conclusions • No spectral curvatures in: • Spectrum of integrated flux density • Overall spectral maps • RM • -21 rad/m2 for southern part foreground • -73 rad/m2 or 290 rad/m2 for the northern part • Internal depolarization at the northern part • Two-SNR scenario • Different properties in the south and north

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